There is one potentially sensitive issue in our relationships with Britain (and Britain's relationship with the EU) that has been obscured, so far at least, by the controversy about the protocol governing relationships between the British mainland and Northern Ireland.
This is simply stated: where does the Border run in Lough Foyle?
Long, long ago – so long ago that neither the UK nor Ireland was a member of what was then called the Common Market – an RTÉ television producer named Odran Walsh created a series of documentaries about different parts of Ireland, the locations chosen – or so some said at the time – by the simple expedient of throwing a dart at a map of Ireland on the wall in Odran's office in Donnybrook.
I was the reporter on one of these adventures. The area chosen by this unusual method was the Inishowen area of Donegal, and in particular that portion of it which bordered Lough Foyle, because Odran's dart had landed in or near Moville.
When we arrived in that picturesque little village, we discovered, to our surprise, that anchored just a few hundred yards off-shore, in the deep-water channel running into Derry, was an impressive collection of heavily armed warships from a number of Nato nations.
Were they in our territorial waters? What price Ireland’s neutrality now? Or so we wondered. And being journalists, we set out to stir up as much trouble as we could.
The documentary, when completed, opened with a panoramic view of the impressive military hardware anchored almost within swimming distance of the Donegal shore, and a lively soundtrack featuring “The Sailor’s Hornpipe”.
We went on to raise this thorny political and perhaps even constitutional issue as best we could, but our attempts to foment local or national controversy met with little response from local people we queried (we frequently encountered the Donegal version of ometà).
The reluctance of local people to express any political opinions about this imbroglio was no bar to their natural instinct for hospitality.
I remember in particular the welcome offered by a local stalwart of the hospitality industry, Mr Diver (pronounced "Divver"). His unusual surname, I assume, was simply a modified Anglicisation of the Irish Ó Duibhir. Mr Diver's expansive and virtually continuous hospitality to the RTÉ team was something from which its members took some time to recover.
The problem was in fact – and remains – more complex than we knew. Even the control of Lough Foyle for fishery purposes remains unclear. A 2007 Act passed by both jurisdictions addressed the problems of both the Foyle and the Carlingford fisheries. This has been superseded by the Belfast Agreement, which created the new Lough Agency.
Problem solved? Not quite, because the foreshore and the seabed in both these areas are excepted matters in Northern Ireland.
It follows from this that a final agreement on the management of the fisheries is dependent on an agreement between the Irish and British governments about who actually owns the Lough.
This is a problem which certainly has not yet been solved, and possibly may not even have been meaningfully addressed.
It may be the case that, under Annex 2 of the NI Protocol to that Agreement, the potential for regulatory divergence on some fisheries and agriculture matters is limited, but anyone with experience of cross-Border legislative and regulatory regimes would not be prepared to bet any substantial amount of money on an early resolution to this issue.
Nor can I imagine the negotiators on either side of this matter approaching the problem with anything like enthusiasm.
What intrigued the members of that RTÉ team, after the documentary was broadcast, was the total absence of any controversy about this issue. Nor has there been the slightest evidence that it has yet figured, or will figure, in any final resolution of the increasingly complex and tendentious Brexit issue.
This, perhaps, provides additional evidence for the theory that Donegal, as well as West Cork, is one of those parts of Ireland whose legislative, social and political context, like that of Hy Brasil, has only a marginal connection with the rest of the island.
And it would not be surprising if some, at least, of its residents are happy enough for it to remain so.